Marshall vs65r blowing fuses

[davorinjo]

Hi people and happy new year to you.
This amp first behaved like this: it wouldn't give out sound until the volume knob was all the way on 5 or so, but when one reached 5 it came on hard, i fear maybe to stressfull on the speaker. Anyway, I plugged my bass guitar into it (it is a guitar amp btw) the other day and obviusly fried something, because the amp now doesn't work at all. It blows a fuse every time I replace one.
I am skilled with soldering iron, but haven't repaired amps yet. I have built some however.
If someone could help with a suggestion of what might be wrong with it, or how to detect the fault I would greatly appreciate it.
-the amp is a ss 65w with a tube in the preamp
-the speaker shows a healthy 6-7 ohms resistance
-I'm including links to schematics
http://www.drtube.com/schematics/mar...65-60-02-1.gif
http://www.drtube.com/schematics/mar...65-60-02-2.gif
http://www.drtube.com/schematics/mar...vs65-61-02.gif

[testlab]

Sounds like bad solder joints. Check any large resistors or radial lead capacitors. Also check the jacks. Component heating can cause solder joints to soften and fracture.
You may need magnification to see solder fractures.